3.3 Harmonics by nonlinear loads

3.2 Voltage swell

Research Trends and Challenges in Smart Grids

appreciated in Figure 8.

of 0.90.

Figure 7.

Figure 8.

Figure 9.

130

Swell distortion power behavior at the SST (a) input and (b) output.

Control response to swell disturbance: (a) HVDC and its reference and (b) modulation index.

In this scenario the grid is disturbed with a swell in the SST input. The swell appears with a voltage increment of 15%Vgrid during a time of 0:05 s (between 0:15≤ t≤0:20). It is considered that there is a load of 800 kVA with a power factor

Figure 7 shows that although the swell disturbance at the SST input, the voltages and currents in the load side are not affected. It is also observed that during the time the swell lasts, the input current decreases. This is attributed to the control of the SST, which keeps constant the output power; this fact can be

Swell distortion waveform behavior: (a) grid voltage, (b) load voltage, (c) grid current, and (d) load current.

For this scenario, a nonlinear load of <sup>z</sup> <sup>¼</sup> <sup>0</sup>:2711^<sup>i</sup> <sup>þ</sup> <sup>0</sup>:2763^<sup>j</sup> and <sup>H</sup> <sup>¼</sup> <sup>0</sup>:233 is connected to the SST. The harmonics generated are the third, fifth, and seventh. These harmonics have impact in voltage waveform of all the components connected into the grid [15] that means the generator will be also affected. Nevertheless, since the SST is connected, the harmonics are mitigated. In Figure 10(a), the voltage waveform distortion produced by the nonlinear load is presented, and Figure 10(b) presents the voltage waveform of the grid, which shows no harmonic disturbances. In addition, it is observed in Figure 11 that the harmonics in the harmonic currents have a negligible impact over the power flow in the grid side.
